Artificial Spin Ice in Exchange-biased Systems

Exchange bias is used to fabricate a hybrid artificial spin ice composed of athermal Fe nanomagnets that are subject to site-specific unidirectional anisotropy, or a local magnetic field, applied in integer multiples of the lattice period along one sublattice of a classic square artificial spin ice (ASI). By varying this period and applying external fields, we demonstrate that the ground state is tunable in this hybrid ASI, and identify three distinct magnetic textures –– a striped ferromagnetic phase, an antiferromagnetic phase, and a state with magnetically charged pairs embedded in an antiferromagnetic matrix.  Monte Carlo simulations broadly support the ground state tunability of this hybrid ASI, and demonstrate that the pinning tunes relaxation timescales and their critical behavior.